<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            height: 200px;
            width: 200px;
            background-color: pink;
        }
    </style>
</head>

<body>
    <div></div>
    <script>
        function getRandomColor(flag = true) {
            if (flag) {
                let arr = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f']
                let str = '#';
                for (let i = 0; i < 6; i++) {
                    let random = Math.floor(Math.random() * arr.length);
                    str += arr[random];
                }
                return str;
            }
            else {
                let r = Math.floor(Math.random() * 256);
                let g = Math.floor(Math.random() * 256);
                let b = Math.floor(Math.random() * 256);
                return `rab(${r},${g},${b})`
            }
        }
        console.log(getRandomColor(false));
        console.log(getRandomColor(true));
        console.log(getRandomColor());
        console.log(typeof (getRandomColor()));
        const div = document.querySelector('div');
        div.style.backgroundColor = getRandomColor();
    </script>
</body>

</html>